Measuring device for a heat flux

ABSTRACT

The invention device ( 100 ) for controlling combustion gases and the thermokinetic characteristics of thermal and chemical reactions of all processes comprises a tubular metallic body ( 1 ) which is closed on the ends thereof with a plug ( 2 ) provided with an input and output ( 8,9 ) and a cap ( 3 ) containing a metallic lens ( 11 ) arranged therein, the lens having a high thermal diffusivity and one of the faces ( 12 ) thereof contacting gaseous fluid ( 22 ). An isotropic chamber ( 5 ) for measuring a radiative flux is disposed inside the metallic body ( 1 ), and a heat flux sensor ( 20 ) is fixed on the median plane of the isotropic chamber ( 5 ).

TECHNICAL FIELD

The present invention concerns a device for measuring a non-stationaryradiating and convective heat flux generated within a gaseous fluid,notably a highly corrosive gaseous fluid under high pressure and at hightemperature such as a gas resulting from the combustion of propellants.

PRIOR TECHNIQUE

Various systems are known for measuring heat flux. One of these systemsis described in the article “Integral Plug-Type Flux Gauge” in NTS TECHNOTES, US Department of Commerce, Springfield, Va., US, 1992, page 34,1-2, XP000287850 ISSN: 0889-8464 and concerns a flux meter, based on theutilization of thermocouples which measure the flux of heat in contactwith a sample of material and by effecting a comparison withconventional gauges. This flux meter works by convection and not byradiation, and does not allow control of unstationary thermal reactionswhich are produced in the gas.

Another system is described in the publication DE 2 064 292, in the nameof SHOWA DENKO KK, which concerns a thermofluxmeter with a heatconducting plate associated with two high heat-resistant plates placedon either side of the heat conducting plate, as well as twothermocouples mounted on either side of the system. It is in fact aclassic auxiliary shell flux meter working by conduction. The responsetime of this type of instrument is too slow for present unstationarysystems in high reactivity gases.

A third system is described in the article by R S Figliola et al“Boundary condition influences on the effective area of a local heatflux probe” which appeared in MEASUREMENT SCIENCE AND TECHNOLOGY, IOPPUBLISHING, Bristol, GB, Vol 7, No. 10 of Oct. 1st, 1996 (1996-10-01)pages 1439-1443, XP000632229 ISSN: 0957-0233 which describes a heat fluxsensor which must be mounted on an isothermal body and which functionsby convection and not by radiation. The transfer by convection implies asignificant reaction time such that the system does not lend itself tothe study of rapid phenomena.

Usually, the control of the combustion of propellants is handled bymeasuring the temperature of combustion gases by means of thermocoupleswhose thermometer pocket is in contact with the gaseous fluid. Howeverthe thermocouple sensors have a relatively long response time andrequire fairly significant contact time with the gaseous fluid. Thesedevices deteriorate very quickly due to this fact in these highlycorrosive gases which are at high pressure and temperature. Besides,with combustion phenomena being highly variable and non-stationary,combustion control tests are of a very short duration and requiremeasuring devices which possesses a low response time. A low timeconstant solution consists of taking an optical measurement of thetemperature through a sapphire window, but the cost of such a device isvery high and the window clouds over very rapidly as a result ofcombustion residue deposits.

In addition to the cost and inadequacy of existing devices, even theprinciple of gas combustion control by temperature remainsinappropriate. In fact, all control systems measure the average gaseousfluid temperature, but temperature is a state quantity and is notrepresentative of the thermokinetics of the combustion gases and thereal state of the gases at each instant of combustion. The control ofthe quantity of heat generated within the combustion gas by the heatflux density magnitude remains the only manner of measuring variablephenomena taking place within the gaseous fluid. Now the phenomena whichoccur within the gases are rapid phenomena which classical temperatureor heat flux measuring systems cannot capture, essentially due to theirexcessively long response times.

DESCRIPTION OF THE INVENTION

The goal of the present invention is to reduce the consequences of theproblems of the existing devices by the creation of a very low responsetime device which enables the instantaneous measurement of heat fluxdensity in a highly corrosive gas environment and under extremetemperature and pressure conditions, while limiting excessive heat fluxsensor deterioration and the resulting costs.

This goal is attained by a measuring device as previously defined,characterized by the fact that it has a tubular metal body open at itstwo extremities, a low heat loss isotropic chamber, mounted coaxiallywithin the tubular metal body, a detector of the radiative heat flux,equipped within the interior of the isotropic chamber, this detectorbeing designed to deliver an electrical signal representative of thenon-stationary and convective heat flux generated within the gaseousfluid, a metallic lens designed to pump the gaseous fluid heat andirradiate it integrally and instantaneously into the isotropic chamber,this lens being mounted on a cap designed to seal one of the extremitiesof the tubular metal body, and a plug designed to seal the otherextremity of the tubular metal body, a space being provided between theisotropic chamber and the tubular metal body to allow the passage of apurging gas circulating within the isotropic chamber and in the space.

Based on the preferred method of construction, the tubular metal body isprovided with a safety vent discharging into the space provided betweenthe isotropic chamber and the tubular metal body and through which thespace accesses the exterior to allow the exit of the over-pressuredpurging gas.

According to this preferred method of construction, the cap is mountedin a removable manner on an extremity of the tubular metal body.

Preferably, the cap has an external thread designed to interact with aninterior thread located on one of the extremities of the tubular metalbody.

In a particularly advantageous manner, the cap is equipped with atransverse opening in which the metallic lens is mounted in such a waythat one of its faces is in contact with the gaseous fluid.

In the preferred production design, the detector and the lateral wallsof the isotropic chamber are integral with the plug and the plug isadvantageously provided with entry and exit paths for the purging gas.

Preferably, the interior wall of the isotropic chamber is coated with ametallic deposit nap so as to ensure a maximum corpuscular reflection ofthe radiated heat flux emitted in the chamber.

In this production design, the exterior wall of the isotropic chamber isalso coated with a metallic deposit so as to reflect a coaxial parasiticray emitted by the tubular metal body in the space provided between theisotropic chamber and the tubular metal body.

The isotropic chamber can be of a cylindrical form and the detector isaffixed according to the axis of this chamber.

The metallic lens is advantageously a high thermometric conductivitybody designed to pump the heat from the heat flux by its face in contactwith the gaseous fluid, its other face being designed to instantaneouslyand integrally radiate the pumped heat flux to the interior of theisotropic chamber.

To this end, the face of the lens in contact with the gaseous fluid canbe coated with a metallic oxide deposit with a high coefficient ofabsorption and resistance to corrosion, the other face being coated witha high emissivity metallic deposit.

The metallic lens is advantageously provided at its periphery with anattachment element by which it is attached in a removable manner to theextremity of the metal body by way of the cap.

In a production variant, the metallic lens can include a circular partby which it pumps the heat flux of the gaseous fluid, and a conical partradiating the heat flux pumped into the isotropic chamber, the two partsbeing joined together by a small diameter connecting axis.

In this production variant, the circular part of the metallic lens canbe of the flat, cylindrical or curved form.

In addition, the conical part of the metallic lens can contain atruncated cavity designed to increase the emitting surface, the conicalpart being full and rounded.

SUMMARY DESCRIPTION OF THE DRAWINGS

The present invention and its advantages will be better understood byreferring to the detailed description of a preferred example ofproduction, provided for information purposes, and not limiting, and tothe attached drawings in which:

FIG. 1 is a sectional schematic view representing the preferredproduction design of the device according to the invention,

FIG. 2 is a schematic sectional view based on a plane normal to thesectional plane of FIG. 1 and representing the device and itspositioning on a support containing the gaseous fluid, during themeasuring process.

FIG. 3 is a sectional schematic view of a variant of the heat fluxmeasuring device according to the invention, and

FIGS. 4A, 4B, 4C and 4D schematically represent several forms of themetallic lens of the invention measuring device.

METHODS OF PRODUCING THE INVENTION

Referring to FIGS. 1 and 2, the non-stationary heat flux measuringdevice 100 shown consists of a tubular metal body 1 closed at one of itsextremities by a plug 2 and at its other extremity by a cap 3 providedwith a traversing central opening 4. A radiative measuring isotropicchamber 5, consisting of a hollow cylinder and equipped with a flat,rectangular detector 20, is attached in a coaxial manner to the interiorof the tubular metal body 1, one of the extremities of the isotropicchamber 5 being connected to the plug 2 and the other extremity of thischamber remaining open. A cylindrical annular space 6 is providedbetween the isotropic chamber 5 and the interior wall 7 of the metalbody 1 in order to permit the evacuation of a purging gas 25. Thispurging gas 25 is preferably low-pressure compressed air which isexhausted in the isotropic chamber 5 in order to maintain thetemperature of the detector 20 as stable as possible throughout theduration of measurement. To this end, the plug 2 is provided with atleast one entrance path 8 for the purging gas 25 and at least one exitpath 9 by which this gas is evacuated in the form of a traversing bore,these paths being realized preferably in the form of traversing bores.The tubular metal body 1 is also provided at one of its extremities withat least one small-diameter vent 10 emerging radially from the annularspace 6, this vent also permitting the discharge of the purging gas 25.This ventilation avoids the risks of overpressure within the device.

A high thermometric conductivity cylindrical metallic lens 11 is mountedin one of the extremities of the metal body 1 coaxially with this bodyby being inserted across the opening 4 of the cap 3. This lens 11 has aslightly curved external face 12 which forms a protuberance with respectto the external face of the cap and an internal face 13 with a truncatedcavity 14 which opens to the interior of the isotropic chamber 5. Theexternal face 12 of the metallic lens is in contact with the gaseousfluid 22 in which the device is found. The lens 11 is also provided witha flange 17 allowing its installation in a removable manner in the lowerextremity of the isotropic chamber 5. To this end, the flange 17 isdesigned to be inserted against the extremity of the metal body 1. It ismaintained in position by the cap 3 which is equipped with an interiorthread 18 a which operates together with an external thread 18 b of themetal body 1 to create a link that can be dismantled. The upperextremity of the lens 11 seals the exit from the isotropic chamber 5 andis equipped with shoulder 15 in order to produce a passage 16 enablingthe evacuation of the purging gas. This passage 16 can also be definedby any other means, for example, by the presence of a beveled edge.

Plug 2 seals the upper extremity of the metal body 1 by a threadedconnection 19, the body being provided with an internal thread and thecorresponding external thread being cut into the external shell of theplug 2. Any other form of connection that can be dismantled can beenvisaged.

Detector 20 is installed at the median plane of the isotropic chamber 5so that one of its extremities is affixed to the plug 2 and crossesthrough it by several millimeters, and so that the other extremity isslightly shortened in relation to the isotropic chamber 5, the lateralsides of the detector 20 being virtually in contact with the interiorwall 31 of the chamber. It is also attached by its lateral sides to theinterior wall of the isotropic chamber 5. This attachment can berealized by any appropriate means.

The heat flux measuring device 100 is connected in a removable mannerthrough the intermediary of the tubular metal body 1 to a support 21containing the gaseous fluid 22 to be controlled. This support can forexample be the shell of a reactor or a turbine, in the specific case ofthe control of gases produced by the combustion of propellants. Part 23of the metal body 1 which is affixed to the support 21 can have anexternal diameter which is greater than or less than that of part 24 ofthe body 1 located outside of the support. The tubular metal body 1 canhave any other appropriate form facilitating the mounting of the variousdevice components and its connection to support 21, its axis beingperpendicular to the direction of flow of the gaseous fluid 22. With theisotropic chamber 5 possessing the same heat radiation properties inevery direction, the orientation of the detector 20 plane with respectto the direction of flow of the gaseous fluid 22 being controlled doesnot affect the measurements of heat flux. This provides flexibility inconnecting the device with a view to measurement.

FIG. 3 represents another form of production of the invention device. Inthis variant, the metallic lens 11 has a significantly different formfrom that of the lens illustrated in FIGS. 1 and 2. This lens 11 has acircular part 26, through which it pumps by convection and radiation theheat flux of the gaseous fluid 22, and a conical part 27 with atruncated cavity 14 by means of which it radiates the quantity of heatreceived into the isotropic chamber 5, the two parts 26 and 27 beingjoined to one another by the intermediary of a connecting axis 28. Thelens 11 is connected to the cap 3 by a pivot linkage, this lens-capsubassembly being affixed in a removable manner to the extremity of themetal body 1 by a screwed connection 29, the cap 3 being provided withan external thread and the metal body 1 with a corresponding internalthread. The metal body 1 can be provided with an external thread 30 bywhich the device is attached to the interior of a corresponding bore(not shown) provided in the gaseous fluid support, the bore beingprovided with a corresponding interior thread.

The removable lens-cap sub-assembly can be easily replaced when the lens11 is worn out by the corrosive action of the gaseous fluid or degradedby working conditions. To this end, various forms of lens 11 can beenvisaged and can be replaced as a function of the parameters of thegaseous fluid 22, the device being calibrated after each replacement.

FIGS. 4A, 4B, 4C and 4D illustrate several other forms of the metalliclens 11. In these different variants, the circular part 26 of the lens,which is in contact with the gaseous fluid 22 to be controlled, can beof a flat form (FIG. 4A), cylindrical (FIG. 4B) or curved form (FIG. 4C)and the conical part 27 radiating the heat in the isotropic chamber 5can present a flat form (FIG. 4A to 4C), circular (not shown) or curvedform (FIG. 4D). It can also be in the form of a hollow cone (FIG. 4A to4C) enabling an increase in the emitting surface.

When the device 100 is properly affixed to the support 21 containing agaseous fluid 22 at high temperature and under high pressure, thequantity of heat generated within the fluid by combustion is pumped bythe high thermometric conductivity metallic lens 11 which, under theheat thrust of the surrounding fluid with which it is in contact, tendsto impose on the common gas-lens interface 12, a temperature close tothe temperature of the lens 11 itself. The temperature discontinuityimposed on the interface being considerable, the gaseous fluid 22therefore more quickly yields, by convection and by radiation, thequantity of heat to the lens 11. The same is true for the face 13 of thelens 11 in contact with the compressed gas 25 purging the isotropicchamber 5. With convection being very weak in this isotropic chamber,the second face 13 of the lens 11 yields by radiation to the gaseousmilieu 25, the quantity of heat received. The detector 20 then deliversan electrical signal proportional to the quantity of heat radiated bythe lens 11. This electrical signal is thus proportional to the heatflux density penetrating the lens 11 through its face 12 and isrepresentative of the variability of heat flux generated in the gaseousfluid 22 to be controlled. Preferentially, the purging gas 25—forexample, low pressure compressed air—is introduced into the isotropicchamber 5 by entrance way 8; it purges the isotropic chamber 5 andleaves through exit 9 by passing via the annular space 6. This enablesthe maintenance of the temperature of the detector 20 as stable aspossible throughout the duration of the measurement.

The interior wall 31 of the isotropic chamber 5 is advantageously coatedwith a polished metallic deposit in order to ensure maximum corpuscularreflection of the radiant rays emitted in the chamber. The interiordeposit can be realized in gold, according to a known vacuum deposit orsimilar process. This material presents only a very weak absorption ofthe radiation emitted. The external shell 32 of the chamber is alsocoated with the same metallic deposit in order to reflect the parasiticcoaxial radiation emitted by the metal body 1 in the annular space 6which creates a heat barrier tending to reduce the conductive andradiative parasitic flux coming from the body.

In addition, the surface of the lens 11 in contact with the gaseousfluid 22 to be controlled, that is, its external surface 12, and itssurface in contact with the purging flux 25, that is, its internalsurface 13, can be coated with a black body. To this end, the externalsurface 12 is coated with a high absorption coefficient metallic oxidein order to improve the resistance of the lens 11 to corrosion, notably,from chlorine, and increase advantageously its life span, and theinternal surface 13 is coated with a high emissivity metallic deposit.

The heat flux measuring device 100 is connected during measurement to aprocessing unit (not shown) by means of electrical cables (not shown).These cables are essentially connected to the electrical circuit ofdetector 20. When the detector is radiated by a quantity of heat fromthe lens 11, it delivers to the processing unit an electrical currentproportional to the density of the heat flux issuing from the lens 11and then, to the non-stationary heat flux generated within the gaseousfluid 22 to be controlled. The processing unit can then calculate theheat flux density within the fluid.

The temperature of the gaseous fluid 22 can then be deduced from thevalue of the heat flux density measured by the Stefan Boltzmann law:T ₀=(f ₁₂φ⁰⁻σ⁻¹ +T ⁴)^(1/4)

in which T₀ designates the temperature of the lens 11, T the temperatureof the radiative flux detector 20, φ₀ the density of the heat fluxpenetrating the lens, σ is the Boltzmann constant, and f₁₂ is the factorfor the device form. This form factor f₁₂ is a calibration factor whichtakes into account the totality of the influences of the variousphysical parameters and those of the construction of the device. Duringcalibration, this factor is adjusted until the temperature indicated bythe processing unit corresponds to that of the target standard used as areference.

Based on the measurement of heat flux, the processing unit can alsocalculate the thermokinetic state indicator of the gaseous fluid 22, theindicator informing in a complete manner on the evolution of combustion.The device according to the invention thus makes availableadvantageously three key data points on the thermokinetics of thecombustion gases, i.e., the heat flux density and the thermokineticstate indicator which are variable quantities, and the temperature whichis a state quantity.

The radiant flux detector 20 mounted in the isotropic chamber is notperturbed by the parasitic convective flux generated by the purginggases 25 of the isotropic chamber 5. The detector 20 must preferably bea differential coplanar couple assembly detector. This type of detectoris commercially available.

The metallic lens 11 of the heat flux measuring device 100 is preferablyfabricated in leather whose thermometric conductivity is very high, thatis, in the order of 36.10³ J/(m².c.s^(1/2)). The isotropic chamber 5according to the preferred production design is 40 mm in length and 5 mmin internal diameter and the lens 11 is 6 mm in diameter with a heightof 6 mm.

INDUSTRIAL APPLICATION POSSIBILITIES

This measuring device can be used for the control of combustion gasesand of any process where control is sought of the thermokinetics aspectof thermal or chemical reactions, notably in nozzles and reactors, andfuel cells for the detection of thermal events such as phase changes.The applications are varied and can be extended notably to petrochemicaland chemical (processes).

1-18. (canceled)
 19. A measuring device for non-stationary radiative andconvective heat flux generated in a gaseous fluid (22), notably a highlycorrosive gaseous fluid under high pressure and at high temperature,such as a gas from the combustion of propellants, the device comprisinga tubular metal body (1) open at two extremities, a low heat-lossisotropic chamber (5) mounted coaxially in an interior of the tubularmetal body (1), a detector (20) of the radiative heat flux, fixed withinthe interior of the isotropic chamber (5), the detector being equippedto deliver an electrical signal representative of the non-stationaryradiative and convective heat flux generated within the gaseous fluid(22), a metallic lens (11) designed to pump heat of the gaseous fluid(22) and radiate the heat integrally and instantaneously into theisotropic chamber (5), the lens being mounted on a cap (3) designed toseal one of the two extremities of the tubular metal body (1) and a plug(2) designed to seal a first of the two extremities of the tubular metalbody (1), an annular cylindrical space (6) located between the isotropicchamber (5) and the tubular metal body (1) to permit passage of apurging gas (25) circulating in the isotropic chamber (5) and in theannular cylindrical space (6).
 20. The measuring device according toclaim 19, wherein the tubular metal body (1) is equipped with a safetyvent (10) discharging into the annular cylindrical space (6) createdbetween the isotropic chamber and the tubular metal body and throughwhich the annular cylindrical space (6) is linked to an exterior toenable discharge of the purging gas (25) in event of over-pressure. 21.The measuring device according to claim 19, wherein the cap (3) ismounted in a removable manner on one extremity of the tubular metal body(1).
 22. The measuring device according to claim 21, wherein the cap (3)has a threaded exterior (18 a) designed to operate with an internalthread (18 b) cut into one of the two extremities of the tubular metalbody (1).
 23. The measuring device according to claim 19, wherein thecap (3) is equipped with a transverse opening (4) in which the metalliclens (11) is mounted in a manner that one of its faces (12, 13) is incontact with the gaseous fluid (22).
 24. The measuring device accordingto claim 19, wherein the detector (20) is affixed to the plug (2). 25.The measuring device according to claim 19, wherein the lateral walls ofthe isotropic chamber (5) are affixed to the plug (2).
 26. The measuringdevice according to claim 19, wherein the plug (2) is provided withentry ways (8) and exit ways (9) for the purging gas (25).
 27. Themeasuring device according to claim 19, wherein an interior wall (31) ofthe isotropic chamber (5) is coated with a metallic deposit nap so as toensure a maximum corpuscular reflection of the radiated heat fluxemitted in the chamber (5).
 28. The measuring device according to claim19, wherein an external wall (32) of the isotropic chamber (5) is alsocoated with a metallic deposit so as to reflect parasitic radiationemitted by the tubular metal body (1) in the annular space(6).
 29. Themeasuring device according to claim 19, wherein the isotropic chamber(5) is in a cylindrical form and that the detector (20) is affixedaccording to an axis of the isotropic chamber (5).
 30. The measuringdevice according to claim 19, wherein the metallic lens (11) is a highthermometric conductivity body designed to pump the heat flux heat via aface (12) in contact with the gaseous fluid (22), an other face (13)being equipped to instantaneously and integrally radiate the heat fluxpumped into an interior of the isotropic chamber (5).
 31. The measuringdevice according to claim 30, wherein the face (12) of the lens (11) incontact with the gaseous fluid (22) is coated with a metallic oxidedeposit with a high absorption coefficient and resistance to corrosion,the other face (13) being coated with a high emissivity metallicdeposit.
 32. The measuring device according to claim 19, wherein themetallic lens (11) is provided at a periphery with an attachment element(17) by which the lens is attached in a removable manner to one of thetwo extremities of the metal body (1) by means of the cap (3).
 33. Themeasuring device according to claim 30, wherein the metallic lens (11)has a circular part (26) through which the heat flux of the gaseousfluid (22) is pumped and a conical part (27) radiating the heat fluxpumped into the isotropic chamber (5), the circular and conical parts(26 and 27) being connected to one another by a small diameter liaisonaxis (28).
 34. The measuring device according to claim 33, wherein thecircular part (26) of the metallic lens (11) has on of a flat,cylindrical or curved form.
 35. The measuring device according to claim33, wherein the conical part (27) of the metallic lens (11) includes atruncated cavity (14) designed to increase an emitting surface.
 36. Themeasuring device according to claim 33, wherein the conical part (27) ofthe metallic lens (11) is full and curved.